So she has some religious beliefs you don't agree with if she is a friend in other regards simply stop discussing religion with her. Arguing why you don't think she should hold her beliefs would be like arguing that a Muslim should eat pork. It doesn't matter what argument you use it won't trump what her religion teaches her. Now if it is her refusing to accept you and your right to hold your own beliefs then you are better off without her.

Leave the much more touchy gay marriage argument and look at the more straightforward you cannot go to heaven argument. I can’t quote chapter and verse but the bible says straight out that acts will not get you to heaven and the only way to get there is though accepting Christ as your savior. That isn’t some crazy concept a fundamentalist church in Texas came up with by misreading a single passage, it is a basic tenant of the Christian religion. It is pretty much on par with Muslims accepting Mohamed was the prophet of god. I would have to say you judging her for that belief shows intolerance on your part not the other way around.

The gay marriage issue is much more complicated since it isn’t verbatim from the bible and it involves actually denying something from other people but it still stems form the same belief system. Do you feel so strongly about the issue that you can only be friends with people who feel the same way? There are issues I feel so strongly about that I won't be friends with people who disagree but they tend to be extreme views and not ones held by significant percentages of the population.

She is right about one thing, you have to watch out for those crazy east coast liberals.